Gray and Muddy Thinking about Global Warming

April 26th, 2006 by group

A more serious problem is that Gray doesn’t even understand that the greenhouse effect works primarily through the effect of greenhouse gases on the top of atmosphere radiation budget, and only very indirectly through the surface budget (as explained in A busy week for water vapor). This compromises almost all of his analysis. For example, many of the supposed changes in surface budget he describes could in fact be due indirectly to changes in greenhouse gases, via their affect on low level atmospheric temperature. By balancing a 4 W/m2 (top of atmosphere) CO2 radiative forcing against changes in evaporation, Gray concludes that the warming from doubling CO2 would be a mere two tenths of a degree C.. He ascribes the weak warming to the lack of water vapor feedback in his calculation, but in fact it is simply due to an incorrect calculation of the energy balance. Standard radiative physics based on a correct treatment of the top-of-atmosphere balance– physics going back at least to Arrhenius– yields a surface warming of about 1C in response to a doubling of CO2, when water vapor feedback is neglected. Gray has committed the major blunder of applying that 4 W/m2top of atmosphere forcing at the surface. In reality, when that radiative forcing is properly applied at the top of the atmosphere, it leads to a warming of the entire atmospheric column which, at the surface, yields a far larger perturbation in the surface energy budget, as we have explained in the above-referenced article.

By the way, Gray discounts water vapor feedback, based on what seems to be a gut feeling on weather systems, plus some unspecified analysis of the NCEP reanalysis dataset (which is completely unsuitable for studying trends in mid tropospheric water vapor); more reliable satellite based studies (e.g. Soden’s study described in A busy week for water vapor ) support a positive water vapor feedback, and even Lindzen seems to be no longer arguing against this feedback.

Claim: Ocean heat storage is inconsistent with CO2 as a cause of warming

Gray also made a mess of an attempt to analyze the mid-twentieth century ocean heat storage. "… the globe underwent a weak cooling between 1950 and 1975 during which CO2 amounts were rising and causing a continuous mean energy gain over this 25 year period of about 0.4 W/m2. If all of this energy went into an accumulation of temperature in the upper 100 m of the global oceans, we would see an upper mean 100 m global ocean temperature increase of 1.1oC. " We are not sure where Gray gets the 0.4 W/m2 radiative forcing figure; the total radiative forcing increase from pre-industrial times to 1975 would be more like .95 W/m2 and it is not a trivial matter to figure out how much to subtract from that to account for the part compensated by ocean warming before 1950; the CO2 radiative forcing increase between 1950 to 1975, on the other hand, would be only .45 W/m2 and the mean new forcing over the period would be about half that. Be that as it may, Gray has not even done the arithmetic right, since .4 W/m2 going into a 100m mixed layer having specific heat of 4200 J/kg and density of about 1000 kg/m3 would only yield a warming of .75C . That’s far from the worst flaw in his calculation, since his two biggest blunders are the neglect of the radiative cooling due to sulfate aerosols (known to be a critical factor in the period in question) and his neglect of the many links in the chain of physical effects needed to translate a top of atmosphere radiative imbalance to a change in net surface energy flux imbalance. In fact, the calculation has been done very carefully by Hansen and co-workers, taking all factors into consideration, and when compared with observations of ocean heat storage over a period long enough for the observed changes to be reliably assessed, models and observations agree extremely well (see this article and this article.).